1. Field of the Invention
The present invention concerns the footwear sector and more specifically it concerns a sole obtainable through compression or injection moulding that allows breathability of the wearer's foot thanks to the combined action of a series of technical elements such as cylindrical stems with relative caps of underlying air chambers shaped like truncated cones and compression distribution devices all located underneath an alternating series of holes moulded on the sole.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
One of the main goals of footwear manufacturers has always been to improve the comfort of their products for users both to facilitate walking and to eliminate the vapour generated inside the shoe due to the perspiration of the foot.
In this sense, in the current state of the art, soles exist that are equipped with an air cushion and with holes to increase comfort and the internal breathability of the shoes, and that have, in fact, been object of numerous patents dating back as far as 1884 with U.S. Pat. No. 302,190 “Air cushion or boot or shoe soles”, which was followed by U.S. Pat. No. 1,044,941 of 19 Nov. 1912; U.S. Pat. No. 1,605,588 of 2 Nov. 1926; U.S. Pat. No. 2,030,545 of 11 Feb. 1936.
More recently, the problem of ventilation inside shoes has been dealt with by fitting, between the foot resting surface and the external sole, a midsole presenting a plurality of equidistant slits the purpose of which is to push the air inside the shoe downwards (U.S. Pat. No. 3,256,621 of 21 Jun. 1966). A similar solution was adopted also by U.S. Pat. No. 5,588,226 of 31 Dec. 1996 entitled “Unidirectional air transfer system for shoes”, drilling in the footbed and in the sole a series of holes designed to facilitate the unidirectional transfer of air between the openings in the footbed and the sole.
Another solution to allow breathability inside shoes is described and claimed by U.S. Pat. No. 5,044,096 of 3 Sep. 1991 entitled “Sole structure or footwear” and consists of a tread sole having microholes formed therein which traverse its whole thickness and is covered by a membrane made of microporous, breathable and waterproof material, preferably Gore-Tex, so as to keep the foot dry and protected from any dampness created by the sweating of the foot or from any water that might have entered through the microholes created in the tread sole.
In any case, the results achieved by the solutions adopted and patented up till the 1990s proved not to be satisfactory as they were not able to guarantee increased ventilation of the foot, nor to prevent the infiltration of water through the microholes in the tread sole.
In particular, the solution described and claimed in U.S. Pat. No. 5,044,096 presents the problem of having to use an extremely thin type of breathable membrane, thereby creating the necessity to protect the said membrane from the abrasive action of the foot during walking with foam material or with polyester felt. This protective material, having a low resistance to compression, loses its thickness through use, tending to flatten irreversibly resulting in a marked loss of comfort in the shoes.
Other materials that are more resistant to compression, e.g. polyurethanes with a high resistance to compression, present the problem of increasing the temperature inside the shoe as they are insulating materials.
In order to overcome the aforementioned problems, other technical solutions were adopted, such as that described and claimed in U.S. Pat. No. 6,209,226 of 3 Apr. 2001 which provides for the adoption of air chambers extending through the whole thickness of the sole formed by elastic spacers and, in any case, such as to create, during walking, an exchange of air under the sole of the foot.
With European patent No. 0975243 the solution to allow breathability of the foot was approached by fitting a series of check valves for the purpose of expelling the air inside the shoe, during walking, through microholes connected with the outside, all equipped with concave values facing the perforated footbed and consisting of a membrane.
Moreover, the air expelling valves referred to in this patent are covered inside the sole by a series of cone-shaped elements positioned at a certain distance from one another and designed to press the air inside them so as to open the valves.
The problem of the aforementioned system is that the cone shape of the elements covering the valves is facing upwards with the effect of creating discomfort to the sole of the wearer's foot also in consideration of the fact that, due to its particular shape, very strong pressure of the foot is required in order to bring about the expulsion of the air.
A further problem of the system referred to in the aforementioned patent is that the air pressure function can only affect that part of the sole in which the wearer's weight is at its maximum.
Another solution is that adopted by U.S. patent application Ser. No. 10/874,213 of 24 Jun. 2004, Publication No. US 2005/0283996 of 29 Dec. 2005, which provided for the creation in the internal part of the sole of a cavity in which to fit a soft membrane consisting of small elastic lamellas preferably rectangular in shape facing towards the bottom of the sole so that the air cushion created in the interspace between the membrane and the concave base of the sole, due to the pressure exerted by the weight of the body on the resting foot and due to the increase in the angle of the lamellas, is expelled to the exterior through a channel realised in the internal structure of the sole equipped with a unidirectional outlet valve.
The problem with the membrane described and claimed in US Patent 2005/0283996 is that the lamellas with which it is equipped tend, with use, to lose their elasticity and break, so that their cushioning effect and the internal ventilation of the foot are limited in time.
Another problem with the above-described solution is that the unidirectional valve may cease to function correctly over time, impeding the discharge of damp air or allowing the infiltration of water in case of rain.